The four Wave Glider robots that set out from San Francisco in November on an unprecedented robotic crossing of the Pacific have arrived at the big island of Hawaii for a quick systems check-up. Their arrival marks the shattering of the world distance record for unmanned wave powered vehicles, as the PacX Wave Gliders, built by California-based Liquid Robotics, have now travelled 6,000 kilometres - and that's just a third of the total 16,500 kilometres they will cover in their total journey.

The previous Guinness World Record for the longest distance traveled at sea by an unmanned system was 4,600 kilometres, a distance the Wave Gliders would have surpassed some time ago. But their arrival - all in good shape - in Hawaii after four months at sea marks a big milestone for the vehicles, which use no fuel and convert the motion of the ocean's waves into forward thrust. Liquid Robotics see them as long-term monitoring platforms that could record data like salinity, acidity, oxygen levels, ocean temperature, and other scientific data relating to climate change and ocean ecology.

Each robot is actually a two-part system consisting of an undersea glider that produces the forward motion connected to a floating section covered in solar cells that power the numerous sensors that take readings every ten minutes. All that data is beamed via satellite back to scientists on dry land, who can use it to maintain a constant idea of what's going on in remote stretches of the Pacific.

After their brief Hawaiian vacation, the quartet will split into two teams, with one bound for the Mariana Trench and then Japan while the other heads across the equator with an Australia-bound heading. They should arrive at their destinations either late this year or early in 2013.